Burner means including flame rod detector with internal electric heating



June 9, 1964 G. G. LLOYD 3,136,353

BURNER MEANS INCLUDING FLAME ROD DETECTOR WITH INTERNAL ELECTRIC HEATINGFiled March 1, 1962 Ac SUPPLY 40 1 FURNACE /7 INVENTOR. FIG. I GRAHAM G.LLOYD .ATTOR Y United States Patent TO f 3 136 353 BURNER MEANSINLUlJING FLAME ROD DE- TECTOR WITH INTERNAL ELECTRIC HEATING Graham G.Lloyd, Hartford, Conn., assignor to Com- This invention relates to aflame detector for detecting the presence or absence of a flame, and inparticular to means for preventing the build-up of deposits ofcombustible material on said flame detector, which deposits can preventthe detector from operating properly.

Wide useis made today of a flame detector comprising a pair ofelectrodes positioned near or adjacent to a burner, whereby the air gapbetween the electrode ends is ionized when a flame is present so that acurrent flows between said electrodes under such conditions. When noflame is present, the air gap is no longer ionized, and there is nocurrent flow between the electrode ends. When no flame is present andcurrent is thus not flowing between the electrodes, an electricalcircuit is broken which normally actuates a light, alarm, or somecontrol element, such as a valve in the fuel line for the burner.

Some fuels, for example oil or black liquor, when being sprayed into acombustion chamber, such as the furnace of a boiler, will be depositedon the surface of the adjacent walls, the burner housing, and theadjacent flame detector. The heat within the furnace will drive off thevolatile constituents, leaving deposits of solid combustible material,such as carbon or sulphur, on such exposed surfaces. If a suflicientdeposit of combustible material forms on the electrodes of the flamedetecting means positioned adjacent the flame, it will prevent currentfrom flowing therebetween, and thus the alarm or control device circuitwill be de-energized, even though a flame may still be present in thefurnace. The presently used method of removing the deposit from theflame detector is to remove such detector from the furnace, clean it,and then place it back into the furnace.

It is an object of my invention to provide means for eliminatingdeposits of combustible material, such as carbon or sulphur, from theflame detecting means, by placing a heater within the flame detectingrod, which heater has a capacity such that it maintains the detectingrod or electrode at a temperature above the ignition temperature of thecombustible material.

The invention will be described with reference to the accompanyingdrawing wherein:

FIG. 1 is a cross sectional side view of a main burner and itsassociated pilot burner; and

FIG. 2 is an enlarged schematic view of the pilot burner shown in FIG.1, incorporating my invention.

Looking now to FIG. 1, numeral depicts the wall of a furnace, forexample the furnace wall of a steam generating unit. A main burner 13extends through a refractory lined opening 12 in the furnace wall 10. Asuitable fuel such as oil is supplied to the main burner by means ofpipe 14. The air necessary to support combustion of the fuel is suppliedby means of air duct 16.

Mounted within the same opening 12 is a pilot burner 17 which is used toinitially light off or ignite the main burner 13. A suitable fuel, forexample gas, is supplied to the pilot burner housing 18 by means of pipe20. The air necessary to support combustion within the pilot burner isalso supplied by means of duct 16. Numeral 22 designates a flamedetecting electrode, and the pilot burner housing 18 forms a secondelectrode. These electrodes detect the presence or absence of a flamewithin the pilot burner, and can be utilized to actuate a light,

3,136,353 Patented June 9, 1964 alarm, ora suitable control element suchas the valve 30, by means of solenoid 32. The electrode 22 is surroundedby suitable insulating sheath 21.

In normal operation, when it is desired to light off the main burner 13,air is allowed to flow through duct 16. Fuel is admitted to the pilotburner 18 through pipe 20, and a suitable igniting means, for example aspark plug 23 ignitesthe fuel issuing from the pilot burner 17. Ifignition of the fuel does not take place within a predetermined shortperiod of time, for example 10 or 15 seconds, the valve 30 is closed tostop the flow of fuel through pipe 20 to the pilot burner 17. If a flameis established at the pilot burner, this flame is detected by means ofelectrodes 18 and 22, and thus the solenoid valve 30 will be held open.After combustion has been established in the pilot burner, a valvewithin pipe 14 is opened, thus supplying fuel to the main burner 13.This fuel is ignited by the flame issuing from the pilot burner 17.After the flame has been established at the main burner 13, the pilotburner can be shut off, since it will no longer be needed until it isagain desired'to light off the main burner unit 13 at some later time. Asuitable flame detecting means (not shown) can then be used to close avalve in the main fuel line 14 in the event that the flame goes out atthe main burner.

Some of the oil issuing from main burner 13 will be deposited on thepilot burner housing 18 and the electrode 22. The heat within thefurnace will drive off the volatile constitutents, thus leaving depositsof solid combustible material, such as carbon or sulphur. If asuflicient deposit of combustible material forms on electrode 22, itwill prevent the electrode from operating properly.

Looking now to FIG. 2, the pilot burner and its associated flamedetecting system embodying my invention is illustrated. As shown, thecircuit for solenoid 32, which actuates valve 30, is completed by theclosing of switch 35. Switch 35 is closed when relay 34 is energized.Relay 34 is tied in with the secondary winding of step down transformer36. In the absence of a flame, the atmosphere between the electrodes 22and 18 forms a sufiicient insulation to prevent a spark or are dischargebetween the electrodes, and in these circumstances no secondary currentexists which will energize relay 34. Timer contacts 37 are for thepurpose of energizing solenoid 32 for 10 or 15 seconds, when the pilotburner is initially being fired. The timer can be one of any well-knowntypes. For example, the initial energi zation of the system can energizea relay having an attached arm carrying a switch. This arm can also beconnected to a pneumatic or hydraulic dashpot. When the relay isenergized, it pushes against the diaphragm of the dashpot, with thebleed of the dashpot being so adjusted that after a predetermined lengthof time (for example, the 10 or 15 seconds referred to above) the switchcarried by the arm has moved a suflicient distance to cause opening ofthe switch, thus de-energizing the circuit through timer 37. When aflame is emerging from the pilot burner 17, the air or atmospherebetween the electrodes is ionized and thus there will be conductionbetween the electrodes, thereby energizing relay 34 and closing switch35.

Normally, without my improved heating element, deposits of solidcombustible material form on the pilot burner housing 18 and theelectrode 22. When a sufficient deposit forms on electrode 22,conduction between the electrodes is no longer possible and the flamedetector fails to perform its function. To prevent this problem fromarising, a heating element 38 is placed within the electrode rod 22,which heating element or resistor is of such a capacity that itmaintains the electrode at a temperature above the ignition temperatureof the combustible material, thus preventing it from depositing on theelectrode. means of electrical source 40 when switch 42 is closed.

The combustible material that normally deposits on the electrodes can beeither sulphur or carbon, and thus electrode 22 should be maintained ata temperature above the ignition temperature of both of these elements.The ignition temperature of sulphur is approximately 500 F,, with theignition temperature of carbon being in the neighborhood of 750 F. Thuselectrode 22 should be maintained at a temperature of 750 F. or higher.

It is not necessary to prevent combustible material deposits fromforming on the burner housing 18. Because of the large area of electrode18, seldom if ever will the entire inner surface of this member becoated up to the point that it will prevent conduction between electrode22 and itself. It should be readily apparent, however, that if twoelectrodes are used, both of which are in the form of rods, it would bedesirable to place a heating element in both of these rods to therebyprevent deposits from forming.

While the preferred embodiment of the invention has been shown anddescribed, it will be understood that such is merely illustrative andnot restrictive.

What I claim is: 7 Ina furnace, main burner means for supplying fuel andair to said furnace, pilot burner means adjacent said main burner meansfor igniting said mainburner As shown, resistor 38 is energized by 7means, flame detecting means comprising a pair of electrodes positionedin the vicinity of the pilot burner means, a source of electrical energyconnected to one of the electrodes, the other electrode beingelectrically grounded, said electrodes being positioned such that when aflame is present between them the air therebetween is ionized andcurrent flows between the electrodes, and when no flame exists betweenthe electrodes the air between them is not ionized and there is nocurrent flow between the electrodes, operable means electricallyconnected in series with the electrodes, said operable means beingindicative of the presence or absence of flame when energized orde-energized, respectively, this operable means being energized orde-energized when a flame exists or is absent, respectively, between theelectrodes, a heater positioned in oneof said electrodes, the capacityof said heater being such that it maintains the electrode at atemperature above the ignition temperature of the fuel, thus preventingthe build-up of fuel deposits on said electrode.

References Cited in the file of this patent UNITED STATES PATENTS2,074,637 Ballentine Mar. 23, 1937 2,374,610 MacLaren Apr. 24, 19452,396,146 Atwater Mar. 5, 1946 2,482,551 Korsgren Sept. 20, 19492,627,308 Clark Feb. 3, 1953 2,721,607 Damon et a] Oct. 25, 1955

